The production of formation sand into a well is a problem when producing, for example, oil or gas, because of its adverse effects on well productivity and equipment. The produced sand often originates from shallow, geologically young formations that have little or no natural cementation to hold the individual sand grains together. As a result, when the wellbore pressure is lower than the reservoir pressure, drag forces are applied to the formation sands as formation fluid is produced. If the formation's restraining forces are exceeded, sand will be drawn into the wellbore.
Operational problems that can arise if a well produces sand include, but are not limited to, erosion of surface equipment, casing or tubular damage, and loss of productivity. Thus, various production and completion practices have been developed to avoid excess sand production. For example, mechanical retention may be used to prevent sand from entering the wellbore flow stream. Mechanical retention relies on sand bridging. That is, certain material is retained to prevent other material from entering the wellbore. Retention of larger particles causes smaller particles to bridge behind them.
One type of device used to restrict sand movement is referred to as a screen. A screen often used in conjunction with a mechanical sand-control technique known as “gravel-packing”. Gravel packing involves running a mechanical device such as a screen into the well and placing accurately sized “gravel” around the screen. The gravel comprises large, clean sand particles. (“Large” refers to its particle size relative to the formation sand particle size.) Such placement of gravel allows the passage of fluids through the gravel and screen, but prevents passage of formation sand into the wellbore flow stream.